In the conventional process of the light-emitting diode (LED), a sapphire (AL2O3) substrate, whose crystal structure is similar to that of Gallium Nitride (GaN), is generally chosen to be a growing substrate. However, the sapphire substrate has the worse electrical conductivity and thermal conductivity, and thus, the GaN LED has the defect that thermal dissipation is poor, the reliability of LED is bad, and the emitting area and efficiency of the LED chip are affected under high-current, high-power and long-time operations. Therefore, the manufacture of LEDs and the raising for the emitting efficiency are hindered.
In order to improve the above-mentioned defects, a conventional method is to remove the sapphire substrate. In the prior art, the nitride semiconductor elements are shifted from the sapphire growing substrate to a bonding substrate by a wafer bonding technique so as to raise the characteristics of the LEDs. Namely, the GaN epitaxial layer is lifted off from the sapphire substrate, and is shifted to a substrate with high electric conductivity and high thermal conductivity. In the above-mentioned process, the laser lift-off technique is usually applied to remove the sapphire growing substrate. However, the laser lift off technique degrades the characteristics of the LED elements and affects the yield thereof. Besides, the laser lift-off technique is high cost. Therefore, if the nitride semiconductor elements can be lifted off from the growing substrate during the wafer bonding process without applying the laser lift-off technique, the manufacturing costs would be highly reduced.
Therefore the applicant attempts to deal with the above situation encountered in the prior art.